Hi guys,
A month ago I bought an Isonic 115 and I am really happy with it.
But I would like to add some lightwind and upwind power, so I am thinking of buying another fin ( I only use it with 8.0 V8 and weigh 75 kgs ).
When the wind is really light ( 11-12 knts ) I find it hard to go upwind.
I know this board is designed for slalom racing, so adding fin will create more drag and reduce speed, but for "allround" sailing ( I mean not racing ) I am thinking of buying one fin in the 44-46 cm range.
1- What do you think ?

Regarding the brand of the fin, I have a chance to buy a Tectonics Spitfire 44 or 46.
2- Do you think is a good fin for the board ?
3- Are the tectonics more powerfull than the curtis ? If this is the case, I think I would go for 44, if not maybe 46. Right ?

In my experience I would not go much bigger fin than 42cm for the Isonic 115. If you go with a 44-46 fin it don&#39;t really make you go a lot better upwind. The balance will be a bit off. A good 40-42 fin will do the job.

Good quality fins is more the key.

I use the Vector Fins Maui the model called Canfire. It works really well on all the Isonic models, and the finish on the fins is always perfect. They have good power, so I recon a 40 cm Canfire would be enough for your Isonic 115 with the 8.0. (This with your weight in mind as well)

On the Isonic 122 I use the 44 Vector Canfire and this is my biggest fin for light wind (upwind and downwind)

I know Pawel (POL 11) used his 42 Canfire on a 135 Isonic with good success as well in the PWA slalom for light wind.

While I&#39;m not in a position to say what size would best suit the iSonic 115, I can say that Tectonic fins are excellent quality fins. I have Goldwings (34cm, 36cm & 38cm), a 46cm Spitfire and a 50cm Mirage. Given the sizing recommended by Jesper Orth above, the F8 Tomcat would be the line you should consider. Actually, it&#39;s the latest updated version of the older Spitfire line. However, if Spitfires are still available in your locale, it clearly remains a worthy choice.

The only thing I can tell you in my experience, is that I test so many fins and finaly notice that the Deboichet SL2 have really big avantage over 38cm. Under some other are really close like Tectonics, but never try the Vector fins.

The reason why we developpe the iSonic with the SL2 Deboichet.

The Tectonics in bigger size like the size you want have less glide and less response. The result is that you get less lift and less top end speed. I recomand you the SL2 40cm.